Source URL: https://blog.trailofbits.com/2024/08/21/yolo-is-not-a-valid-hash-construction/
Source: Hacker News
Title: "YOLO" is not a valid hash construction
Feedly Summary: Comments
AI Summary and Description: Yes
Summary: The text discusses common cryptographic missteps made by clients, particularly focusing on the use of poorly constructed hash functions and message authentication codes (MACs) referred to as “YOLO constructions.” It emphasizes the security risks associated with these ad-hoc approaches and advocates for established cryptographic standards, thus providing valuable insights for security professionals in ensuring proper implementation of hashing and key derivation functions.
Detailed Description:
The text provides an in-depth analysis of common pitfalls—referred to as “YOLO constructions”—in cryptographic practices. It highlights the dangers associated with creating ad-hoc approaches to hashing and MAC functions, which can lead to serious security vulnerabilities. The author brings attention to several specific constructions and offers alternatives backed by established cryptographic standards, underscoring the importance of adhering to known solutions to enhance security.
Key Points:
– **Common Crypto Missteps**: The text reveals that many clients resort to creating their own hashing or MAC solutions when faced with specific problems, leading to insecure implementations that neglect foundational cryptographic principles.
– **YoloMultiHash**: This flawed approach involves hashing multiple values concatenated with a separator. The primary issue is ambiguous encoding, where two different inputs can produce the same hash, violating collision resistance.
– **Secure Alternatives**: It suggests using established functions such as TupleHash from SP800-185 or BLAKE3, which offer secure solutions for hashing multiple values while avoiding common pitfalls.
– **YoloMAC**: This construction is prone to length-extension attacks, allowing attackers to append garbage data and manipulate the message’s MAC. The text warns about ambiguous encoding issues, leading to potential forgery.
– **Established Mechanisms**: The author recommends well-known protocols like HMAC, KMAC, or built-in mechanisms available in cryptographic libraries to prevent length-extension and encoding issues when designing MAC systems.
– **YoloPBKDF**: This weak key derivation function (KDF) presents significant vulnerabilities, including susceptibility to brute-force attacks. The text criticizes its simplicity and advises the use of modern KDFs like Argon2 or scrypt for better security.
– **Memory-Hard Functions**: Highlighting the importance of using memory-hard functions, the text discusses how imposing a memory requirement can greatly hinder an attacker’s ability to perform parallel key derivations, thus improving security.
– **Summarization and Guidance**: The concluding remarks encourage professionals to avoid reinventing the wheel by leveraging existing, well-researched cryptographic solutions rather than creating custom, potentially insecure implementations.
Overall, this analysis serves as a crucial reminder for security and compliance professionals in AI, cloud, and infrastructure security to prioritize using robust, vetted cryptographic practices and standards over ad-hoc solutions that could expose their systems to avoidable risks.